The present invention is directed to sensoring apparatus which find utility in measuring various aspects of liquid mediums. More specifically, the invention provides a means of enhancing the effectiveness of an amperometric sensor which utilizes a semi-permeable membrane to separate the internal elements and the electrolyte contained therein (and enveloping the elements) from the media being sampled, monitored or analyzed. In this regard reference is hereby made to U.S. Pat. Nos. 3,510,421; 3,577,332; and 3,929,603 which are hereby incorporated by reference and which comprehensively describe the type of measurements or analysis which are commonly made utilizing these means. In addition, these patents also disclose the type membranes commonly used in the sensors.
With respect to certain type sensors, particularly the halogen sensing cells, the present inventor determined that certain problems existed which effected the overall accuracy and measuring sensitivities. These problems were due, it was discovered, to a defect in the sensors; namely, a loss in the electrolyte concentration within the cell due to the electrolyte's flow from the cell through the membrane to the medium which contained the ion to be measured, and the resulting dilution (as the medium flowed inward through the membrane to replace the lost electrolyte). Cells that were constructed which provided a simple open path between the cathode and anode exhibited short life because of the aforementioned occurrences. It also was noted that these sensors provided "noisy outputs", i.e., electronic noise in the nature of spurious signals, which effected the overall sensitivity and accuracy of the measuring device.
Generally, the present inventor discovered that if the electrolyte contained within the cell reservoir was forced to communicate between the anode and cathode of the cell by diffusion through a porous material (plug) placed adjacent to the cathode and in contact with the cell's membrane, not only was electrolyte concentration loss or dilution controlled but also electronic noise was substantially eliminated. The invention will become more apparent from the description of a typical arrangement of the cell parts which follows, together with the descriptive matter directed to the improvement. Also, the description of the cell as per the explanation of the drawing will serve to highlight the invention.
The cell comprises
(i) an electrically non-conductive body having an electrolytic reservoir therein, PA1 (ii) a pair of spaced electrodes positioned in said reservoir and adapted to be joined by an electrolyte in said reservoir, PA1 (iii) an opening communicating between said reservoir and the exterior of said body, PA1 (iv) a thin flexible polymeric membrane permeable to said constituent and said electrolyte, and PA1 (v) mounting means maintaining said membrane under tension over one electrode which is supported in the face of the electrically non-conductive element which is disposed in said opening and which is in a position to close said opening, wherein said opening is slightly larger than said electrode and the face of the electrically non-conductive element supporting such and the portion of the opening remaining being fitted with a porous material to provide a tightly fitting barrier between said membrane, said electrolyte in said reservoir and said electrodes, and said porous material preferably but not necessarily contacting said membrane and being permeable to said electrolyte so as to permit electrical communication between said electrodes.